is not plural used for single person for respect?
– qdinarSep 7 '15 at 9:19

@qdinar, you inquired a useful query. Actually it is seen that in some or even many languages or cultures many people use the plural form instead on the single, in order to respect ... / But, to the best of my knowledge, now and then it is used in Arabic as well, BUT: less than other cultures. (in limited positions, I reckon)
– اللهم صل علی محمد و آل محمدDec 6 '15 at 8:00

Even "Assalam o Alaikum" could be used for women, it is more convenient to use "Assalam o Alaikun" ( without the appended -a ); unless you want to say another thing else without stopping, then you can use "Assalam o Alikuna (oh mothers/sisters or something else)". I wish it helps.

According to Arabic grammar, KOM is used for men, and Kon (Konna) is used for women. As a result if you’d like to use the correct grammatical shape of it, you ought to say “Assalam o Alaikon (Konna) which is written like the following phrase:

السلام علیکن

Of course, there is another nice point, and it is related to singular and plural nouns. Actually “Kon” is related to plural noun (according to the correct Arabic grammar).

As much as I see, it can use for both men and women in informal form. But if you are looking for the formal form of the greeting or saying salam for women, you should be aware that if there are more than 2 women, you should say Assalamo Alaikon.

There is another important matter that you can note, and that is about two women. In fact if there are two women, you should say Assalamo alaikoma in the form of formal and in fact according to the true grammar of Arabic.